User:Tom Gluick/glutamine synthetase/Assignment 8

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Assignment: My Intent
Assignment 8: IIIB: Central-loop: Map the interactions involving the central loop that stabilize quaternary structure. Explain how these interactions contribute to quaternary structure stability.

My hope and intent: I hoped the students would map the interactions the central loop makes with other components in Glutamine synthetase using the information in PDBsum as a guide. Comments upon how the the various interactions lead to stabilizing the complex would be left to their imaginations.

Student Contribution
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Glutamine synthetase is composed of twelve subunits, formed as two hexameric rings. The two rings are held together by twelve central loops TextToBeDisplayed which extend into the central region of the complex and include a small, four stranded β loop TextToBeDisplayed. Each loop is 33 residues long and has a convex shape. The spatial orientation TextToBeDisplayed of the loops has been found to be less accessible for interactions to occur, contributing to the catalytic activity of the enzyme.

The central loop (residues 156-188) is a site where covalent modifications, with inhibitory effects are found. This segment of the complex is subject to proteolysis by four secreted proteases, which cleave specific residues. Another covalent modification known to occur at central loop of Glutamine synthetase is ADP-ribosylation of Arg-172 TextToBeDisplayed.

It is evident then that the central loop of glutamine synthetase (residues 156-188) is an important component of the enzyme, anchoring the subunits together and providing the spatial orientation necessary for activity. Therefore the central loop contributes both to the function and stabilization, via numerous hydrophobic interactions TextToBeDisplayed and four different hydrogen bonding interactions TextToBeDisplayed of the quartenary structure of Glutamine synthetase.

References:
1.  Fisher, M. T., Stadtman, E. R., Oxidative Modification of Escherichia coli Glutamine Synthetase, The Journal of Biological Chemistry, 1992, Vol 267. No3, 1872-1880

2.  Moss, J., Stanley, S., Levine, R. L., Inactivation of Bacterial Glutamine Synthetase by ADP-ribosylation, The Journal of Biological Chemistry, 1990, Vol. 265, No. 34, 21056-21060

3.  Yamashita, M. M., Almassy, R. J., Janson, C. A., Cascio, D., Eisenberg, D., Refined Atomic Model of Glutamine Synthetase at 3.5 A Resolution, The Journal of Biochemistry, 1989, Vol. 264, No. 30, 17681-17690

Authors
Kary Atkinson Murteza Shahkolahi Annette Zeender

Assessment
The presentation had strong points and weak points. One strong point is that the students produced a few fabulous visuals showing that students are capable of exercising their imagination while working with SAT. These students were effective at using background colors, colors, transparency and other commands to produce eye-catching visuals. Also, like other equally effective and better presentations, the material was organized well. One weak point is that these students had some difficulty with the WIKI script as the green links contain the default language. I do remember when meeting with other groups that other students had some intitial difficulty with the syntax of the script. I feel there is enough information available for students to write the script properly. Another weak point is that the visuals fail to effectively make the point presented in the the text; for instance see the last green link. The link that shows the Arg 172, the site of ribosylation fails to show where it is located in the subunit or the complex. This seemed to be a general failing on both mine and all students' part: I tried to emphasize that the various regions of GS to be discussed ought to be first presented in the GS complex, then the subunit and if necessary presented by itself. I must have failed in conveying this effectively.